Heat exchangers of the plate type are comprised of pairs of preformed plates joined to other pairs at their ends by integral bosses and separated at their middle section by air centers or corrugated fins, the plates and fins all being brazed together so that each pair of plates becomes a tube for carrying refrigerant, the bosses serving as a manifold for permitting refrigerant flow from one tube to another, and the fins facilitating heat exchange between the tubes and air flowing outside the tubes. U.S. Pat. No. 4,470,455 issued to Sacca describes such a plate type heat exchanger in detail. The assembly of the plate type heat exchanger elements into a core ready for brazing has typically been carried out largely by hand operations. Specifically, the first step is to assemble a fin element between two plates and crimp the plates together into subassemblies where their bosses connect, and then manually stack such subassemblies into a fixture which holds each subassembly in place. It is desirable to improve on the assembly practice by an improved method and machine for assembly. In particular it has been found that the process is improved in terms of automation and in terms of reducing spacing in the fixture if it is begun by joining the plates together before adding fins. It is desirable to have a machine to perform the assembly operations to reduce the manufacturing expense and otherwise improve the efficiency of the assembly practice. It has been demonstrated that the machine assembly of plate pairs is practical.